Add missed "marked" in package.json

[ruv]

The "marked" package is missed in package.json

[GeraldWodni]

This website is based on kern.js, which already has marked as a dependency

[ruv]

I see, thank you. I tested the code without kern.js and was therefore a little surprised.

Since I had a probably wrong assumption: if a module is used independently of kern.js, it should be declared in package.json independently too.